I am a Conan x Ai fan. They make each other a better person.
(And they just met! The timeline in Manga is not yet a year!)
Maybe there is no obvious sign that Conan loves Ai, but he really tried his best to offer Ai a nice and comfortable life; and vice versa. And there is chemistry in the air.
Shinichi's most important life goal is to become a detective which means he will be in danger at any rate;
However, Ran does not like investigation. Though Ran's parents and Shinichi like detective works, Ran does not. Not for the past 17 years, and not in the future. Ran's life goal is to become a general housewife, love her husband, and teach her child. When Shinichi is not near, she always think he might meet some pretty girls, but the truth is, Shinichi is only busy at work. It would be a hard life for these two if they ends up together. Ran needs a man who stays at home more often, and gives her the love she wants.
ShinRan could be a wonderful and beautiful childhood memory; however, not for happily ever after. Ran's parents is an example. They love each other, but they can't live together.